Human microbiota consists mostly of bacteria but also includes viruses, molds, yeasts, and protozoa which colonize skin and mucous membranes of cavities exposed to the exterior, such as the gastrointestinal, respiratory and genitourinary tracts. In these environments, microbiota establishes a symbiotic relationship with the host, providing early modulation of the host’s physiological development, nutrition, immune and pathogen resistance functions in all stages of life. [1,2] Therefore dysbiosis in the microbiota has been associated with diseases as inflammatory bowel disease, multiple sclerosis, diabetes, allergies, asthma, autism, and cancer [3, 4, 5, 6, 7].

Initially lungs and airways were omitted from organs to be studied because there was a common belief that healthy lungs were sterile, but recent data has changed the sterile theory of the lungs: the respiratory tract contains microbial communities from the nasal fossae to the pulmonary alveolus, with the highest concentrations found in the upper airways. [8] [9] This autochthonous microbiota contributes to the defense against colonization and infection by pathogens in the respiratory mucosa and thereby prevents their spread throughout the tract. So, in healthy conditions lungs microbiota consists of a transient community of microorganisms, mainly from the nasopharynx and oropharynx, which settle down in lungs establishing an apparent homeostasis with the host.[10]

It is not clear if microorganisms found in the lungs are unique but most data suggest substantial diversity in healthy individuals. [11, 12, 13, 14]

Recent data has also shown that the presence of specific microbe (e.g. Treponema Whipplei) in the lungs of healthy subjects was not found in upper airway samples and the evidence that colonization of the lower airways with this microbe was enhanced in immunodeficiency state. [15] These findings suggest that unique taxa could find a special niche in the lung environment and exert an immunomodulatory role. [16]

Even if the role of the gut microbiota in shaping the mucosal immune system is clearly understood, it remains unclear whether the observed associations with lung microbiota and immune system are causal or not. [17, 18]

Otherwise, there is a relationship between gut and lung microbiota known as “gut-lung axis” and acting on this connection, pharmacological treatments with probiotics are under study processes to verify if modifiers of gut microbiota can also influence lung microbiota and the pulmonary pathologies, especially in critical hills. [19,20, 21]

On this basis, our research team at the University of Foggia (Italy) aims to study the effects of nutrition treatment in traumatic brain injured patients in the Intensive Care Unit on lung microbiota to seek to better how this new treatment can influence the outcome in these specific patients.

Authors: Antonella Cotoia, Giuseppe Ferrara, Lucia Mirabella, Gilda Cinnella – University of Foggia (Italy)

References:

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